Implantable medical devices (IMD's) such as pacemakers and implantable cardioverter defibrillators are frequently utilized in monitoring and regulating various conditions within the body. An implantable cardioverter defibrillator, for example, may be utilized in cardiac rhythm management applications to monitor the rate and rhythm of the heart and for delivering various therapies such as cardiac pacing, cardiac defibrillation, and/or cardiac therapy. In some cases, the implantable medical device can be configured to sense various physiological parameters occurring in the atria and/or ventricles of the body to determine the occurrence of any abnormalities in the operation of the patient's heart. Based on these sensed parameters, the medical device may then deliver an appropriate treatment to the patient.
Communication with implantable medical devices is often accomplished via a telemetry link between an external device and an implanted medical device such as a pulse generator. Typically, telemetric communication between the external device and the pulse generator is accomplished using an inductive or RF link. An example inductive link utilizes an inductive coil which, when energized by an external voltage source, produces an inductive field that can be used to transmit communications signals and/or charging signals to the implanted device. An example RF link, in turn, utilizes dynamic RF (i.e., electromagnetic waves) to transmit communications signals and/or charging signals to the implanted device. In some techniques, telemetric communication between the external programming device and the implanted device can be accomplished using an acoustical link provided by an ultrasonic transducer. Other telemetry methods have also been employed for coupling external devices to implantable medical devices.
Due to their size, conventional IMD's are typically implanted in remote regions within the body away from the source of the signal or the target of the therapy. In some cardiac rhythm management applications, for example, the IMD is implanted in the pectoral or abdominal region of the patient, and includes leads that provide an interconnect between the IMD and the other devices implanted within the body. In some cases, it may be desirable to sense physiological parameters or therapeutic functions at a location within the body having a limited space or volume, requiring the packaging, battery, and associated electronics to be made small to reduce device size.